THE SYNTHESIS OF CONDENSED RING COMPOUNDS. XIII. THE PREPARATION OF 5- AND 6-CARBALKOXY-1,4-TOLUQUINONES. ADDITION OF 5-CARBOMETHOXY-1,4-TOLUQUINONE AND 6-CARBOMETHOXY-1,4-TOLUQUINONE TO BUTADIENE1
A highly enantioselective, quinoneDiels-Alderreaction catalyzed by chiral samarium and gadolinium pyridyl-bis(oxazoline) (pybox) complexes has been developed. The reaction scope has been extended to include three quinones and five dienes, all of which exclusively provide the expected endo product in excellent yields and enantioselectivities.